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Ford 9N, 2N & 8N Discussion Forum
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Re: head bolt question

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Author  [Modern View]

01-28-2013 17:22:19

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heybusdriver said: (quoted from post at 20:23:54 01/28/13) I laid it on my bench in the dark with a
flashlight shining , I measured the light gap with
a square .Sorry meant 5/ 1000 , not 5mm , old head
measured 20/1000. Since I took a closer look at
the salvaged head in the daylight and find out the
spark plugs are seized in the hole, I am soaking
now with +deep creep", if that doesn't loosen them
I'll try heat from my torch tomorrow.

9N 222933

2N with 8N motor 8N345567

8N 146710

8N 179555

8N 197904

8N 199000

8N 254079

8N 362039

Measure the gap with a feeler gauge.

I'd like to address Zane's point. You can bend any cylinder head including a big thick warped cast iron OHV V8 head an awful lot by tightening down the head bolts. If you have any doubt just ask a machinist that has to clamp them to a machine table to resurface them. If the table surface isn't dead flat the head will bend when it is clamped down. Then after its machined and the clamps are released it will spring back and the freshly machined head won't be flat anymore.

So if we can easily bend any head when we tighten teh head bolts what's the big deal with being flat to start with? Simple - every pound of head bolts force that is used to bend the head back down towards flat is a pound of clamping force lost at the head/block junction. In other words using a warped head reduces the gasket clamping force and increases the potential for a head gasket failure. OK you say - why not just use a little higher tightening torque to up the force from the bolts and compensate for the loss diue to warpgae? Maybe but the standard head bolt torque value is already close to the limit the bolts can handle and you are now blindly guessing about how much more you need. That risks coming up short or over stretching and permanently deforming the head bolts making matters even worse. You can wind up with a warped head AND even less clamping force where you actually need it.

That's the engineering issues. In practice a flat head does as Zane says bend a lot easier than a big thick OHV head so it can tolerate a bit more warpage. How much more is the million dollar question. The "official" warpage tolerance on a cast iron OHV head is usually about ,005. I have never seen an official Ford specification for the flathead but .020 is more than I personally would risk. In other words you pays your money and you takes your chances using anything that isn't very nearly factory flat from the git-go. You are re-engineering Fords carefully calculated clamping numbers while flying in the dark - how lucky do you feel today?

This post was edited by TheOldHokie at 17:26:54 01/28/13.

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01-28-2013 17:48:11

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 Re: head bolt question in reply to TheOldHokie, 01-28-2013 17:22:19  
"measure the gap with a feeler gauge"

that's exactly what I did, I measured the gap with a feeler gauge by laying my square against the head. I could clearly see the amount of light shining through the gap.

I thought I was being quite clear about what I meant.
I thought 5mm is the same thing as 5/1000. I thought mm is 1000. When you say 20/1000 is a lot , hmm I gap my front mount distributor @ 15 ,side mount distributor @25, spark plugs @25 , doesn't seem like a lot to me. I may be wrong, I'm just a back yard N tractor mechanic.

9N 222933
2N with 8N motor 8N345567
8N 146710
8N 179555
8N 197904
8N 199000
8N 254079
8N 362039

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01-29-2013 04:01:37

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 Re: head bolt question in reply to heybusdriver, 01-28-2013 17:48:11  
Stan, No disrespect intended here, but you need to use a straightedge (machined flat) to measure gaps like you mentioned. A square is not flat enough for precision measuring. Again no disrespect intended. Gerard

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01-28-2013 18:04:28

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 Re: head bolt question in reply to heybusdriver, 01-28-2013 17:48:11  
Quoting Removed, click Modern View to see

Sorry but I misunderstood your explanation of how you measured the gap. If .020 sounds OK to you go for it. The worst that can happen is you will get a chance to do it over again.


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